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 A217217 Dimension of totally primitive elements of the algebra "Baxter" of order n. 0
 0, 1, 0, 1, 4, 19, 96, 511, 2832, 16215, 95374, 573837, 3520228, 21961119, 139038824, 891817687, 5787091552, 37946582995, 251173847170, 1676831257693, 11282156358500, 76453813499219, 521508969157826, 3578990500062417, 24700214881378152, 171359711873508367 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 REFERENCES S. Giraudo, Algebraic and combinatorial structures on pairs of twin binary trees, Journal of Algebra, Volume 360, 15 June 2012, Pages 115-157. LINKS Table of n, a(n) for n=0..25. S. Giraudo, Algebraic and combinatorial structures on Baxter permutations, DMTCS proc. AO, FPSAC 2011 Rykjavik, (2011) 387-398. FORMULA Giraudo gives a generating function. PROG (PARI) baxter(n) = sum(k=1, n, binomial(n+1, k-1) * binomial(n+1, k) * binomial(n+1, k+1) / (binomial(n+1, 1) * binomial(n+1, 2))); lista(m) = {u = t + t*O(t^m); b = 1 + sum(n=1, m, baxter(n)*u^n); gfbt = (b-1)/b^2; for (n=0, m, print1(polcoeff(gfbt, n, t), ", ")); } \\ Michel Marcus, Feb 16 2013 CROSSREFS Cf. A001181. Sequence in context: A122394 A047781 A089354 * A083315 A301417 A025573 Adjacent sequences: A217214 A217215 A217216 * A217218 A217219 A217220 KEYWORD nonn AUTHOR N. J. A. Sloane, Oct 03 2012 EXTENSIONS More terms from Michel Marcus, Feb 16 2013 STATUS approved

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Last modified August 5 05:32 EDT 2024. Contains 374935 sequences. (Running on oeis4.)